Conventionally, cathode ray tubes have been used mainly as image display apparatuses for color televisions, personal computers and the like. However, in recent years, image display apparatuses have been required to be miniaturized, and made lighter and thinner. In order to satisfy these demands, various types of thin image display apparatus have been developed and commercialized.
Under these circumstances, various types of thin image display apparatus have been researched and developed recently. In particular, liquid crystal displays and plasma displays have been developed actively. The liquid crystal displays have been applied to various types of products such as portable personal computers, portable televisions, video cameras, carnavigation systems and the like. In addition to that, the plasma displays have been applied to products such as large-scale displays, for example, 20 inch-displays or 40-inch displays.
However, problems of such a liquid crystal display include a narrow visual angle and a slow response. Regarding a plasma display, high brightness can't be obtained and the consumed electricity is large. A thin image display apparatus called a field emission image display apparatus has attracted considerable attention to solve these problems. The field emission image display apparatus uses field emission, or a phenomenon in which electrons are emitted in a vacuum at room temperature. The field emission image display apparatus is a spontaneous luminescent type, and therefore it is possible to obtain a wide visual angle and high brightness. Further, the basic principle (to illuminate a fluorescent substance with electron beams) is same as that of a conventional cathode ray tube, and therefore a picture with natural color and high reproduction can be displayed.
The above-mentioned type of a field emission image display apparatus is disclosed in Unexamined Published Japanese Patent Application (Tokkai-Hei) No. 1-100842. Another image display apparatus disclosed in Tokkai-Hei No. 2-33839 is known as a spontaneous light emission type image display apparatus with high-quality images, which is different from the above-mentioned field emission image display apparatus in the structure but uses a linear hot cathode.
FIG. 7 is a perspective exploded view showing a first conventional image display apparatus (refer to Tokkai-Hei No. 2-33839). As shown in FIG. 7, the conventional image display apparatus comprises a back electrode 100, a linear cathode 101, an electron beam-attracting electrode 102, a control electrode 103, a first focusing electrode 104, a second focusing electrode 105, a horizontal deflecting electrode 106, a vertical deflecting electrode 107, a front glass container 109a having a fluorescent layer 108 on the inner surface, and a rear glass container 109b. The back electrode 100, the linear cathode 101, the electron beam-attracting electrode 102, the control electrode 103, the first focusing electrode 104, the second focusing electrode 105, the horizontal deflecting electrode 106 and the vertical deflecting electrode 107 are contained between the rear glass container 109b and the front glass container 109a (the fluorescent layer 108 side), and the space where those components are contained between the glass containers (109a, 109b) is maintained under vacuum.
In the image display apparatus, electron beams are formed in a matrix by the linear cathode 101 and the electron beam-attracting electrode 102, and focused by using the first focusing electrode 104 and the second focusing electrode 105. The electron beams are further deflected by the horizontal deflecting electrode 106 and the vertical deflecting electrode 107 before being landed on predetermined positions of the fluorescent layer 108. The control electrode 103 controls the electron beams over time, and adjusts each electron beam independently according to picture signals for displaying pixels.
FIG. 8 is a cross-sectional view showing the schematic structure of a second conventional image display apparatus (refer to Tokkai-Hei No. 1-100842). As shown in FIG. 8, the conventional image display apparatus comprises an electron emission source 210, fluorescent layers 208a and 208b, a faceplate 209 and a transparent electrode 207. The fluorescent layers 208a and 208b are provided on the faceplate 209 via the transparent electrode 207 and the fluorescent layers 208a and 208b face the electron emission source 210 in parallel. The electron emission source 210 comprises a substrate 204, a thin film 202 formed on the substrate 204 and electrodes 201a and 201b, which are provided for applying a voltage to the thin film 202. An electron emission part 203 is provided by processing the thin film 202.
According to the above-mentioned image display apparatus, the deflection of electron beams emitted from the electron emission part 203 is adjusted by controlling a voltage applied to the electrodes 201a and 201b, and the deflected electron beams are landed on predetermined positions of the fluorescent layers 208a and 208b to illuminate these fluorescent layers. The conventional image display apparatus is also provided with a flat electrode (not shown in FIG. 8) between the electron emission source 210 and the fluorescent layers (208a, 208b). In the disclosed technique, the voltage applied to the flat electrode is lower than that of the transparent electrode 207 in order to focus the electron beams on the fluorescent layers by utilizing the lens effect. Since the flat electrode is designed only to adjust the deflection degree for the inherently-deflected electron beams, it does not function to deflect the electron beams actively.
The respective components for the image display apparatuses in the conventional technique are thin and flat. Therefore, a combination of these components can form a thin image display apparatus having a flat screen.
In the image display apparatus according to the conventional technique, however, errors will occur during manufacturing or assembling the respective components. Such errors will affect directly the deviation of the landing position of an electron beam. For example, in an image display apparatus where one pitch of an electron source corresponds to one stripe pitch of the fluorescent layer, 10 .mu.m deviation of the electron source results in 10 .mu.m deviation of the position that the electron beam is landed on the fluorescent layer. Accuracy variations such as deviation of the deflection electrode and differences in level will also result in direct influences on the deviation of the landing positions for the electron beams. Therefore, in such an image display apparatus, landing an electron beam on a predetermined position of a fluorescent layer is difficult when the positions of the components comprising the electron sources and the deflection electrode are deviated. As a result, more inconveniences such as overlap irradiation may occur, and thus, the image quality of the image display apparatus will deteriorate, and an image display apparatus with high resolution cannot be easily obtained.
In order to improve the resolution of an image display apparatus, electron beams should be further focused (i.e., a spot diameter of an electron beam should be reduced), and the electron beam should be landed on a fluorescent layer with higher accuracy. In a conventional image display apparatus, however, a remarkable improvement cannot be obtained because of the structural limitations, even by using regular actions including deflecting actions. For example, the spot diameter should be decreased to 1/5 and also the landing accuracy, to 1/5 or less in order to improve the solution by 5 times, which is considerably difficult in the conventional technique.